Preform extrusion molding apparatus, method for extrusion molding, and preform

ABSTRACT

A process includes: supplying a main resin from outer and inner flow channel, to a joined flow channel at a predetermined supply velocity for a predetermined time; supplying a second resin from a middle flow channel to the joined flow channel simultaneously with the main resin at a predetermined supply velocity for a certain time within the predetermined time; and sliding a shut-off pin to bring the pin forefront to a predetermined position near an outlet of the inner flow channel, open to the joined flow channel, before the second resin is supplied, or during a time starting after a time from the start of the second resin supply and ending with the termination of the supply, so that the velocity of main resin supply from the inner flow channel to the joined flow channel is reduced to a predetermined level by adjusting the degree of aperture for the outlet.

This application is a divisional application of application Ser. No.15/868,720 filed Jan. 11, 2018, which in turn is a divisionalapplication of application Ser. No. 14/359,154 filed May 19, 2014 (nowU.S. Pat. No. 9,956,707), which in turn is a U.S. national stageapplication of PCT/JP2012/078662 filed Nov. 6, 2012. The disclosures ofthese prior applications are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to a device and a process for injection molding apreform in a test tube shape for use in the biaxial stretching and blowmolding of a synthetic resin bottle having an intermediate layerlaminated with main-resin layers that make up a shape of the preform,and to the preform made by these device and process.

BACKGROUND ART

Polyethylene terephthalate resin bottles (PET bottles), obtained bybiaxially stretching and blow molding an injection molded preform in atest tube shape, have high transparency, high mechanical strength, and ahigh gas barrier property, and find their way into various fields suchas beverages, foods, and cosmetics. There are many cases where thequality of a content fluid has to be prevented from decreasing, andthere are use applications especially requiring a gas barrier propertyagainst oxygen and other gases. In such cases, a 2-resin/3-layer laminarstructure is used for the bottle in which an intermediate layer made of,e.g., a nylon resin having a high gas barrier property is laminated withthe main-resin layers of a PET resin that makes up the shape of thepreform. The PET bottle having a laminar structure of this type can bemolded by biaxially stretching and blow molding a preform having a testtube shape and a 2-resin/3-layer laminar structure.

Patent document 1 describes an invention associated with a moldingdevice having a multi-layer nozzle for injection molding a2-resin/3-layer preform such as described above. As an example, FIG.10(a) shows a prior-art preform 101 of this type. FIG. 11 is a schematicvertical section of a nozzle section 11 in a device for molding thepreform 101. FIG. 12 is an explanatory diagram showing an example of theinjection pattern used with this molding device to mold the preform 101.FIG. 13 is an explanatory diagram showing the filling steps in which themold cavity is filled with molten resins.

The preform 101 in FIG. 10(a) has a gas barrier resin layer 101 b madeof a resin having a high gas barrier property as an intermediate layerand laminated with the main-resin layers. This preform 101 is biaxiallystretched and blow molded into a bottle having a function that isdifficult for a single PET resin to achieve, for example, a function ofcontrolling the oxidative degradation of the content by minimizing thevolume of outside oxygen that penetrates the bottle. Such a bottle canbe made from the preform 101.

The preform 101 having such a laminar structure is molded by using aninjection pattern shown in FIG. 12 and a molding device having amulti-layer nozzle section 11 shown in FIG. 11. Now referring to thedevice of FIG. 11, a PET resin supplied from a first feeder Sa passesthrough an outer flow channel 15 a and an inner flow channel 15 c, andflows into a joined flow channel 19. A barrier resin supplied from asecond feeder Sb passes through a middle flow channel 15 b and entersthe joined flow channel 19. At that time, the barrier resin Rb is putbetween the outer flow channel 15 a and the inner flow channel 15 c.Inside the joined flow channel 19, a joined resin fluid is formed inwhich the barrier resin Rb is laminated with the main resin Ra in acylindrical shape. This joined resin fluid is then injected into acavity 4 of a mold 1 to fill the cavity.

An example of injection molding is described, now referring to FIGS. 12and 13. FIG. 13(a) shows a state right before point E in the injectionpattern shown in FIG. 12. In this state, it is found that only the PETresin Ra have been filled. At point E, the injection of the barrierresin Rb is started. Between point E and point F, the barrier resin Rbis sandwiched between layers of the PET resin Ra, and is sent to themold cavity in that laminated state (See FIG. 13(b). At point F, theinjection of the barrier resin is terminated, and from then on, thecavity is filled only with the PET resin Ra until the end of theinjection step (See FIG. 13(c)). Thus, the preform 101 shown in FIG.10(a) can be obtained.

PRIOR ART REFERENCES Patent Document

Patent document 1: Japan patent application publication No. 2004-330672

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As can be seen from FIG. 10(a), an entire peripheral wall of the preform101 thus molded is not necessarily laminated with the barrier resinlayer 101 b, but in many cases, the barrier resin layer 101 b is notlaminated in an upper portion of the neck 102 and in the bottom 106 ofthe preform 101.

In the case of the neck 102 which is an open end, the barrier layer 101b should not be laminated in the upper portion of the neck 102 becauseof a problem of deformation. If the barrier layer 101 b made of adifferent resin were extended to the upper end, the cylindrical neck 102would deform into an elliptical shape at the time of molding shrinkageor thermal crystallization treatment of the neck 102. In the example ofthe preform 101 shown in FIG. 10(a), the leading edge, LE, of thebarrier resin layer 101 b is located at a nearly middle height of theneck 102, because of the consideration for the above-describeddeformation, gas barrier property, and in addition, the material cost ofthe barrier resin. Thus, a high degree of accuracy is required tocontrol the position of the leading edge, LE, of the barrier resin layer101 b. But the neck 102 is a portion having a relatively thick wall, anddoes not deform after the preform 101 has been biaxially stretched andblow molded into the bottle. Even if a limited area of the upper portionof the neck 102 is made of only the PET resin layer 101 a, any decreasein the gas barrier property of the entire bottle can be restricted to arelatively low level.

Unlike the neck 102, the bottom 106 is a portion which is stretched to athin wall. From a point of view of preventing the decrease in the gasbarrier property of the entire bottle, it seems preferable to cover theentire bottom 106 with the barrier resin layer 101 b, as shown in FIG.10(b). However, it is necessary for the flow of the barrier resin intothe cavity 4 to be cut instantaneously at point F in the injectionpattern of FIG. 12, i.e., at the end of injection of the barrier resin.If this fails, the lamination would fall in a blunt-edged state, inwhich more than one barrier resin layer 101 b may be laminated in thebottom 106, or fractions of the barrier resin layer 101 b, or theso-called scales, may exist in the bottom 106. Because of such anon-uniform state of the barrier resin layer, the bottom of the bottle,when molded, may deform irregularly to give an unstable ground contact.Another problem is that the mechanical strength of the bottle may fallto a low level. Still another problem is that a fraction of the barrierresin Rb may stay behind in an open end portion of the multi-layernozzle section 11. This fraction would mix in the PET resin Ra in thenext shot.

According to a molding process that enables the bottom to beencapsulated, it is possible for the barrier resin layer 101 b to form acontinuously laminated wall without segmenting the bottom 106, as shownin FIG. 10(b). But still problems remain, as vestige of the gate locatedat the center of the bottom 106 of the preform is unstable in size,causing unstable moldability. Furthermore, the stretching rod may runthrough the inner PET resin layer 101 a on the inner side at the timewhen the preform is vertically stretched, thus giving damage to thebottle.

This invention has been made to solve the problems found in prior-arttechniques associated with the injection molding of preform in which asecond resin layer is laminated with, and embedded in, theabove-described main-resin layers. Thus, a technical problem of thisinvention is to control the behavior of the intermediate layer in thelamination of the preform bottom so as to achieve the biaxial stretchingand molding at high productivity and to offer a bottle having a high gasbarrier property given by the intermediate layer.

Means of Solving the Problems

This invention relates to a device for injection molding a preform, aninjection molding process using this device, and a preform that can bemolded by this injection molding process. Descriptions will be madebelow in an order of the injection molding device, the injection moldingprocess, and the preform. A main feature associated with the injectionmolding device of this invention is a device for injection molding apreform in a test tube shape for use in biaxial stretching and blowmolding, in which preform a second-resin layer serving as anintermediate layer is laminated with layers of a main resin that makesup the shape of the preform, the device having a nozzle section forforming a joined resin fluid by allowing a second resin for forming thesecond-resin layer to join a main resin for forming the main-resinlayers, and having a mold disposed ahead of the nozzle section, saidnozzle section comprising:

three cylindrical layer-forming flow channels including an outer flowchannel, a middle flow channel, and an inner flow channel in anoutside-to-inside order, and

a joined flow channel connected to these three flow channels andextended to a head of the nozzle section, wherein the main resin ispassed through the outer and inner flow channels, and the second resinis passed through the middle flow channel, and

a rod-like shut-off pin disposed on an inner side of the inner flowchannel and slidably inserted therein, wherein an outlet of the innerflow channel, which is open to the joined flow channel, is shut off oropened, and a degree of aperture can be adjusted, by controlling theposition of a forefront of the shut-off pin.

Another feature of this invention is that in the above-described mainfeature, the device comprises a first resin feeder for feeding the mainresin and a second resin feeder for feeding the second resin, the nozzlesection comprising in an outside-to-inside order the three flow channelsincluding the outer flow channel, the middle flow channel, and the innerflow channel, and a cylindrical joined flow channel connected to thethree flow channels and extended to the head of the nozzle section,wherein the main resin from the first feeder is sent to both the outerand inner flow channels, and the second resin from the second feeder issent to the middle flow channel, and wherein the two resins are joinedtogether in a cylindrical shape to form a joined resin fluid in jointflow channel, which fills a cavity by being injected into the cavity byway of a pin gate disposed at a position of the cavity of the moldcorresponding to the center of a bottom wall of the preform.

According to the injection molding device having the above-describedfeatures, the cylindrical shut-off pin is slidably inserted inside theinner flow channel, so that the position of the forefront of thisshut-off pin can be controlled to shut off or open the outlet of theinner flow channel, which is open to the joined flow channel, and toadjust the degree of aperture to be opened. Because of this shut-off pinforefront position control, the resin supplies from the outer, middle,and inner flow channels to the joined flow channel can be controlled inthe following manner, while continuing the resin supplies from the firstand second feeders:

1) When the inner flow channel is fully opened by locating the forefrontupstream of the outlet of the inner flow channel which is open to thejoined flow channel, the second resin supplied from the middle flowchannel is sandwiched between the main-resin layers coming from both theouter flow channel and the inner flow channel, and this takes place inthe joined flow channel so that the joined resin fluid thus formed inthe joined flow channel would have the second resin laminatedcylindrically with the columnar main resin.

2) When the forefront is located at a predetermined position near theoutlet of the inner flow channel to decrease the degree to which theoutlet is opened and to slow down the speed of the main resin supplyfrom the inner flow channel, the second resin in a columnar main resinwould have a layer width less than in the case of 1).

3) When the forefront is located downstream of the outlet of the innerflow channel, in order to shut off the inner flow channel completely,the second resin supplied through the middle flow channel joins with themain resin coming only from the outer flow channel because the supply ofthe main resin from the inner flow channel is completely shut off. Inthat case, the joined resin fluid formed in the joined flow channelconsists mainly of the main resin with the second resin being laminatedin a thin-wall cylindrical shape.

As described above in 2), it is possible for the second-resin layerinside the main resin of the joined resin fluid to be controlled with ahigh degree of accuracy so that the second-resin layer would have apredetermined diameter in the cylindrical shape. Especially, at thebottom of the preform, the intermediate layer can be laminated with ahigh degree of accuracy which has been difficult in the prior art.

Since the above described feature is based on a simple mechanism oflinear sliding movement of the shut-off pin, the degree of aperture tobe opened can be adjusted for the inner flow channel with predeterminedtiming by means of high-accuracy positioning.

Still another feature associated with the injection molding device ofthis invention is that in the above-described features, the inner flowchannel has a diameter-reduced flow channel in an end portion, where thediameter is reduced in a tapered manner to a level adequate for thejoined flow channel.

According to the above-described feature, the degree of aperture, towhich the inner flow channel is shut off or opened, can be adjusted forthe outlet of the inner flow channel with high accuracy by the forefrontof the shut-off pin which makes effective use of the diameter-reducedflow channel.

Still another feature associated with the injection molding device ofthis invention is that in the main feature described above, the slidingmovement of the shut-off pin is controlled by a servomechanism.

According to the feature described above, the inner flow channel can beshut off or opened with predetermined timing, and furthermore, theposition at which the forefront of the shut-off pin is located, can becontrolled with high accuracy, by using the servomechanism to controlthe sliding movement of the shut-off pin. Thus, the degree of aperture,to which the inner flow channel is shut off or opened, can be adjustedwith high accuracy by the forefront of the shut-off pin.

A main feature associated with the process for injection molding apreform according to this invention is a process for injection molding apreform for use in the biaxial stretching and blow molding, whichpreform has a test tube shape and has a second-resin layer laminatedwith main-resin layers made of a main resin that makes up the shape ofthe preform. The injection molding process of this invention comprisesthe steps of:

a) using the above-described injection molding device of this invention;

b) supplying a main resin from an outer flow channel and an inner flowchannel to a joined flow channel at a predetermined supply velocity fora predetermined period of time;

c) supplying a second resin from a middle flow channel to the joinedflow channel simultaneously with the main resin at a predeterminedsupply velocity for a certain period of time within the predeterminedperiod of time; and

d) sliding the shut-off pin to bring the pin forefront to apredetermined position near an outlet of the inner flow channel, whichis open to the joined flow channel, previously before the second resinis supplied, or during a period of time starting after a predeterminedtime from the start of second-resin supply and ending with thetermination of the supply, so that the velocity of main resin supplyfrom the inner flow channel to the joined flow channel is reduced to apredetermined level by adjusting the degree of aperture for the outletend.

Another feature associated with the process of this invention forinjection molding a preform is that in the main feature described above,the process comprises the steps of.

a) at first, keeping the outlet of the inner flow channel at a fullyopen state by means of the control of a sliding position of the shut-offpin, and supplying the joined flow channel with the main resin from thefirst feeder by way of the outer and inner flow channels;

b) supplying the second resin from the second feeder to the joined flowchannel from the inner flow channel by way of the middle flow channelfor a certain period of time at a predetermined time after the start ofmain resin supply, and allowing the second-resin layer to be sandwichedbetween the main-resin layers coming from the outer flow channel and theinner flow channel;

c) bringing the forefront of the shut-off pin to a predeterminedposition near the outlet of the inner flow channel, which is opened tothe joined flow channel, in a predetermined time after the start of themain resin supply from the inner flow channel, so as to decrease thevelocity of the main resin supply from the inner flow channel; and

d) then, in a predetermined time after the end of the main resin supplyfrom the inner flow channel, sliding the shut-off pin to keep the innerflow channel pressured in a fully open state for a predetermined time.

Still another feature associated with the process of this invention forinjection molding a preform is that in the main feature described above,the process also comprises:

a) joining the main resin and the second resin in the joined flowchannel to form a joined resin fluid, and injecting the joined resinfluid into the mold cavity by way of a pin gate disposed at a positionof the mold cavity corresponding to the center of a bottom wall of thepreform in order to fill the cavity with the fluid; and

b) setting an injection pattern, including a speed of the main resinsupply, a starting time, an ending time, and a speed of the second-resinsupply, a moment of sliding the shut-off pin, and the positioning of theforefront of the pin, associated with a degree of aperture to be openedor closed at the outlet of the inner flow channel, and thereby,positioning a trailing edge of the second-resin layer within apredetermined range in the bottom, while excluding the gate vestige tobe formed at the center of the bottom, which is molded in asemi-spherical shell shape when the second-resin layer is laminated withmain-resin layers to form a preform.

According to the above-described molding process of this invention, ajoined columnar resin fluid is formed in a sequential manner in thejoined flow channel in process steps described below.

(1) The main resin from the outer flow channel joins the main resin fromthe inner flow channel in the joined flow channel to form a joinedcolumnar resin fluid comprising only the main resin.

(2) Then, the second resin from the middle flow channel flows betweenthe main resin from the outer flow channel and the main resin from theinner flow channel to form a joined resin fluid in which the cylindricallayer of the second resin has been sandwiched between the two columnarlayers of the main resin.

(3) At this point, the degree of aperture for the outlet of the innerflow channel is adjusted by the forefront of the shut-off pin to reducethe speed of main-resin supply from the inner flow channel so that thejoined resin fluid is formed in such a way that the second resin wouldhave a thin, cylindrical shape and a predetermined diameter.

(4) Lastly, with the termination of the second-resin supply from themiddle flow channel, the main resin from the outer flow channel joinsthe main resin from the inner flow channel to form again the columnarjoined resin fluid made of the main resin.

The step (3) described above is a step for controlling in asophisticated manner the behavior of lamination that forms thesecond-resin layer near the bottom of the preform. According to themolding process described above, the second resin can maintain acylindrical laminar shape as far as the trailing edge, because themain-resin supply from the inner flow channel continues, even in a smallamount, until the second-resin supply terminates. This continued supplyof the main resin serves to prevent encapsulation in which a continuouslaminate pattern is formed in the entire bottom region including a gatevestige. The cylindrical laminate shape of the second resin caneliminate the problem of insufficient moldability caused byencapsulation and the problem of deformed bottom of the bottle.

In addition, the adjustment of aperture for the outlet of the inner flowchannel also enables the second resin to have a cylindrical laminateshape and a predetermined diameter, at least, at or near the trailingend. Thus, when the intermediate layer of the second resin is laminatedwith the main-resin layers, it becomes possible to have highlysophisticated control over the lamination pattern, which involvessetting the trailing edge of the second-resin layer at a position in apredetermined range near the bottom of the preform, while excluding acircular pin gate vestige formed at the center of the bottom wall plate.

The main feature of the molding process described above has thefollowing description: “previously before the second resin is supplied,or during a period of time starting after a predetermined time from thestart of the second-resin supply and ending with the termination of thesupply.” As understood from this description, the timing of adjustingthe degree of aperture for the outlet of the inner flow channel by meansof the forefront of the shut-off pin can before the starting time of thesecond-resin supply or during the period of supply. As described above,in order for the highly sophisticated control over the laminationpattern for the second-resin layer at a position near the bottom of thepreform, it is necessary to maintain a lamination pattern in which thesecond-resin layer inside the joined resin fluid is in a slim,cylindrical shape at or near the trailing edge of the second-resinlayer. It is also necessary to adjust the degree of aperture for theoutlet of the inner flow channel at least until the supply of thesecond-resin layer comes to an end.

Still another feature of the injection molding process of this inventionis that in the main feature described above, a synthetic resin having ahigh gas barrier property is used as the second resin so that thesecond-resin layer is effective as a gas barrier layer.

A main feature associated with the preform of this invention is atest-tube-like preform for biaxial stretching and blow molding use, inwhich an intermediate layer of a second resin laminated with themain-resin layers that make up the shape of the preform. The preform ischaracterize in that the trailing edge of the second-resin layer islocated in the bottom within a range covering from outside of an outerperipheral edge of a circular gate vestige formed in the center of abottom plate of a bottom to a peripheral edge of a corresponding innerperipheral surface of a body.

It has been difficult for the conventional molding technology to achievesuch a lamination pattern for the second-resin layer near the bottom,but it becomes possible to achieve by means of the injection moldingprocess of this invention. When the trailing edge of the second-resinlayer is located in a limited range in the bottom except for the gatevestige, the second-resin layer can fully perform the function of gasbarrier and the like, while resolving the problems of bad moldability ordeformation in the bottom of the bottle, such as

Effects of the Invention

According to the injection molding process using the injection moldingdevice of this invention, the adjustment of aperture for the outlet ofthe inner flow channel also enables the second resin to have acylindrical laminate pattern having a predetermined diameter, at least,at or near the trailing end. In addition, it becomes possible to havehighly sophisticated control over the laminate pattern, which involvessetting the trailing edge of the second-resin layer at a position in apredetermined range near the bottom of the preform, while excluding acircular pin gate vestige formed at the center of the bottom wall plate.The second-resin layer at such a position can fully perform the gasbarrier function and the like, while resolving the problem of badmoldability or the problem of deformation in the bottom of the bottle,which is caused by covering the gate vestige with the second-resinlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a front view, with a partially taken vertical section, andFIG. 1(b) is a bottom view, respectively, of the preform of thisinvention.

FIG. 2 is a schematic explanatory diagram showing a vertical section ofan important part of the injection molding device of this invention inan embodiment.

FIG. 3 is an explanatory diagram showing a position of movement of theshut-off pin inside the device of FIG. 2.

FIG. 4 is a vertical section showing an outline structure of the mold.

FIG. 5 is an explanatory diagram showing an example of the injectionpattern used in the injection molding process of this invention.

FIGS. 6(a)-6(c) are each a schematic explanatory diagram showing stepsof filling the mold cavity with molten resins using the injectionpattern of FIG. 5.

FIGS. 7(a)-7(c) are each a schematic explanatory diagram showing thesteps of filling the mold cavity with molten resins using anotherinjection pattern.

FIG. 8 is a table showing compiled results of measurements for thepositions of trailing edge of the second-resin layer in 5 examples ofpositions to which the forefront of the shut-off pin has moved.

FIG. 9 is a front view of a bottle biaxially stretched and blow moldedfrom the preform of FIG. 1.

FIG. 10(a) is a front view, with a partially taken vertical section, ofan example of a conventional preform; and FIG. 10(b) shows an example ofanother preform.

FIG. 11 is a cross-sectional view schematically showing an example of aconventional multi-nozzle section.

FIG. 12 is an explanatory diagram showing an example of the injectionpattern for molding the preform of FIG. 10(a).

FIGS. 13(a)-13(c) are each an explanatory diagram showing the steps offilling the mold cavity with molten resins using the injection patternof FIG. 12.

MODES FOR CARRYING OUT THE INVENTION

The preform, the injection molding device, and the injection moldingprocess of this invention will be described below with respect topreferred embodiments, now referring to the drawings, in which FIG. 1shows an embodiment of the preform 101 of this invention molded by thelater described injection molding process of this invention. The preformgenerally has a test tube shape and a laminar structure in which abarrier resin layer 101 b, i.e., an intermediate layer made of a secondresin, is laminated with PET resin layers 101 a, i.e., the main-resinlayers that occupy a major portion of the preform. In this embodiment,MXD6 nylon is used as the barrier resin. The preform 101 has a totalheight of 100 mm. A body 105 has an outer diameter of 20 mm and anaverage wall thickness of 2.5 mm. The preform weighs 22 g. A circulargate vestige 107, with a diameter of 5 mm, remains at the center of theouter peripheral surface of the bottom 106 (See FIG. 1(b)).

The leading edge, LE, of the barrier resin layer 101 b is located at alength, La, of 19.3 mm, which is a distance from the top surface of theneck 102. The trailing edge, TE, of the barrier resin layer 101 b islocated at a length, Lb, of 5 mm, which is a distance from the center ofthe bottom plate of the bottom 106, i.e., located peripherally at about2.5 mm outside of the outer peripheral edge of the gate vestige 107. Asseen in the bottom view of FIG. 1(b), it is found that the trailingedge, TE, is located in a range covering from outside of an outerperipheral edge of the circular gate vestige 107 formed at the center ofthe bottom plate of the bottom 106 to a lower end of an inner peripheralsurface 105 p of the body 105. Both lengths La and Lb are averagevalues.

FIGS. 2, 3, and 4 schematically show an example of the injection moldingdevice of this invention, in which FIG. 2 is a vertical section of anozzle section 11 and its vicinity, with a mold 1 being fitted on thedownstream side; FIG. 3, an explanatory diagram explaining a position ofthe forefront 20 p of the shut-off pin 20 in the device of FIG. 2; andFIG. 4, a vertical section schematically showing a structure of the mold1.

This nozzle section 11 has a first mandrel 21, a second mandrel 22, anda third mandrel 23, which are all cylindrical and are disposedconcentrically in an order from inside to outside. A shut-off pin 20 ina rod shape is disposed inside of the first mandrel 21 in a slidablyinserted manner. The fore-end of each mandrel has a tapered portion, thediameter of which is reduced toward the downstream. A main resin Raflows through a cylindrical outer flow channel 15 a, which is formedbetween the third mandrel 23 and the second mandrel 22. A second resinRb flows through a cylindrical middle flow channel 15 b, which is formedbetween the second mandrel 22 and the first mandrel 21. In addition, themain resin Ra also flows not only through the outer flow channel 15 abut also through a cylindrical inner flow channel 15 c, which is formedbetween the first mandrel 21 and the shut-off pin 20.

The main resin Ra is supplied from a first feeder Sa, which comprises anextruder of a screw type or an accumulator having a plunger fitted tothe tip of the extruder, passes through a guide channel 12 a and flowsthrough an outer flow channel 15 a and an inner flow channel 15 c by wayof manifold 14 al and 14 a 2, respectively. The second resin Rb issupplied from a second feeder Sb, passes through a guide channel 12 band flows through a middle flow channel 15 b by way of manifold 14 b.

Then, the main resin Ra enters a diameter-reduced flow channel 15 asdisposed in an end portion of the outer flow channel 15 a. The mainresin Ra also enters a diameter-reduced flow channel 15 cs disposed atthe end of the inner flow channel 15 c. The second resin Rb enters adiameter-reduced flow channel 15 bs disposed in an end portion of themiddle flow channel 15 b. All these resins enter a joined flow channel19 where the main resin Ra and the second resin Rb join together to forma joined resin fluid. This joined resin fluid is passed through a pingate 5 disposed at a position corresponding to a center of a bottomplate of the bottom 106 of the preform 101, and is injected into acavity 4 to fill this cavity 4, which is formed by a core mold 2 and acavity mold 3 of a mold 1.

In the device of this invention, the shut-off pin 20 forms the innerflow channel 15 c together with the first mandrel 21, and is allowed toslide through the inner peripheral surface in a diameter-reduced headportion of the first mandrel 21. This shut-off pin 20 performs anordinary function of shutting off or opening the head portion of thenozzle section 11. In addition, when the forefront 20 p of the pin 20 iscontrolled to take a predetermined position near an outlet 17 c of theinner flow channel 15 c that is open to the joined flow channel 19, thepin 20 can adjust the degree of aperture of this outlet 17 c between afull open state and a shut-off state so as to adjust the amount of themain resin Ra to be supplied from the inner flow channel 15 c to thejoined flow channel 19. The sliding movement of the shut-off pin 20 (inthe vertical direction in FIG. 2) is controlled by a servomechanism (notshown) utilizing a servomotor, to ensure that the highly sophisticatedflow-adjusting function described above can be performed.

As described above, the shut-off pin 20 adjusts the speed of the mainresin Ra supplied from the inner flow channel 15 c, and since thisadjustment is carried out at the outlet 17 c of the inner flow channel15 c, i.e., a point of contact with the joined flow channel 19, anydelayed time caused by the visco-elastic quality of molten resins can beavoided, and the supply and shut-off of resins and the flow rateadjustment can be controlled in a high degree of accuracy, as comparedto a conventional flow-adjusting function using a check valve or a spoolvalve disposed at a position remote from the joined flow channel 19 onthe upstream side of the nozzle section 11.

FIG. 3 is a diagram for explaining the position of the forefront 20 p ofthe shut-off pin 20 in the device of FIG. 2. In FIG. 3, a givenposition, Ls, of the forefront 20 p is expressed as a length fromposition Ls1 in the end portion of the nozzle section 11. Position Ls1is a position corresponding to an upstream end of the diameter-reducedflow channel 15 cs. For the device of this embodiment, Ls1 is 18 mm fromthe position Ls0

An example of the injection molding process of this invention will bedescribed below. FIG. 5 is a schematic explanatory diagram showing aninjection pattern used when the preform 101 shown in FIG. 1 is injectionmolded by using the injection molding device of FIG. 2. This pattern isdepicted using a lateral axis as a time axis and a vertical axis asspeeds of molten resin supplies. The solid line shows the injectionpattern for the PET resin Ra, which is the main resin, and the dottedline shows that of the barrier resin Rb. The PET resin Ra is suppliedfrom the first feeder Sa at a supply velocity of 7.1 g/sec. The barrierresin is supplied from the second feeder Sb at a supply velocity Vb of0.53 g/sec.

Along with the above-described injection pattern, FIG. 5 also shows theposition of the forefront 20 p of the shut-off pin 20 found over time bya two-dot chain line. In a time zone of Sp (Ls1), the forefront 20 p islocated at Ls1, i.e., 18 mm; and in a time zone of Sp (Ls), theforefront 20 p is located at 14.55 mm in the case of this embodiment.The flow rate is controlled by narrowing down the degree of aperture atthe outlet 17 c of the inner flow rate 15 c so that the supply of thePET resin Ra would be reduced. As regards the time axis, the injectionstarting time ta1 for the PET resin Ra is used as a benchmark. Theinjection ending time ta2 for the PET resin Ra is 4.5 sec. For thebarrier resin Rb, the injection starting time tb1 is 1.6 sec, and theending time tb2 is 3.4 sec. The forefront 20 p of the shut-off pin 20 islocated at the position of 14.55 mm for a period ranging from time ts1(2.1 sec) to ts2 (3.9 sec).

The injection molding steps over time in the injection pattern of FIG. 5are as follows:

(1) Set the forefront 20 p of the shut-off pin 20 at the position of Ls1(See FIG. 3) to fully open the outlet 17 c of the inner flow channel 15c, and supply the PET resin Ra from the first feeder Sa to the joinedflow channel 19 by way of the outer flow channel 15 a and the inner flowchannel 15 c.

(2) Supply the barrier resin Rb from the second feeder Sb to the joinedflow channel 19 at time tb1 by way of the middle flow channel 15 b, andflow the barrier resin Rb between the PET resin Ra from the outer flowchannel 15 a and the PET resin Ra from the inner flow channel 15 c.

(3) At time ts1, reduce the supply speed for the PET resin Ra sentthrough the inner flow channel 15 c, where the forefront 20 p of theshut-off pin 20 takes the position Ls (See FIG. 3).

(4) Terminate the supply of the barrier resin Rb from the second feederSb at time tb2.

(5) Bring the forefront 20 p of the shut-off pin 20 back to the positionLs1 at time ts2 to allow the speed of the supply of the PET resin Racoming from the inner flow channel 15 c to return to the original speed.

(6) Reduce the mold pressure to a predetermined level at time ta2(resulting in a decrease in the speed of supply from the first feederSa), and keep the pressure at that level till time ta3.

FIGS. 6(a), 6(b), and 6(c) are schematic explanatory diagrams showingthe steps of filling the cavity 4 of the mold 1 with the PET resin Raand the barrier resin Rb in the above-described steps of the injectionpattern of FIG. 5. The filling of the cavity 4 proceeds in the order of(a)→(b)→(c) in FIG. 6. On the right side of (a), (b), and (c), there aregiven cross-sectional views taken from lines J1-J1, J2-J2, and J3-J3.These cross-sectional views show separately the PET resin suppliedthrough the outer flow channel 15 a as Ra1, and the PET resin suppliedthrough the inner flow channel 15 c as Ra2.

When the barrier resin Rb is supplied through the middle flow channel 15b as described above, a reduced feed rate is used for the PET resin Ra2from the inner flow channel 15 c. Therefore, as seen in FIG. 6(a), thebarrier resin Rb is laminated with the PET resin layers Ra1 and Ra2 in aslim, cylindrical shape with a small diameter. If the filling iscompleted in the state shown in FIG. 6(c), passing through the state ofFIG. 6(b), under this laminated condition that the barrier resin Rbtakes a small, cylindrical shape, then like the preform 101 in FIG. 1,the trailing edge, TE, of the barrier resin layer 101 b would have alength Lb of 5 mm from the center of the bottom 106, and the trailingedge, TE, can be allowed to come close to the outer peripheral edge ofthe gate vestige 107.

FIG. 7 is also a schematic explanatory diagram showing the steps offilling the cavity with the PET resin Ra and the barrier resin Rb, butin this case, the preform is injection molded while the forefront 20 pof the shut-off pin 20 is kept at the Ls1 position of 18 mm withoutmoving the forefront 20 p in the injection pattern of FIG. 5. Thisembodiment corresponds to a comparative example wherein theabove-described Ls is set at 14.55 mm. Filling of the cavity 4 proceedsin the order of (a)→(b)→(c). Like in FIG. 6, the cross-sectional viewstaken from lines K1-K1, K2-K2, and K3-K3 are shown on the righthand sideof the respective vertical sections

The injection molding based on the injection pattern, wherein theforefront 20 p is kept at the length Ls1 of 18 mm, is similar to aconventional molding process shown in FIGS. 11-13. When the barrierresin Rb is supplied from the middle flow channel 15 b, there is nochange in the rate of supply of the PET resin Ra2 from the inner flowchannel 15 c. Therefore, as can be seen in FIG. 7(a), the barrier resinRb is in a cylindrical shape having a large diameter when the barrierresin Rb is sandwiched between the PET resin layers Ra1 and Ra2. Whenthe filling operation passes through the state of FIG. 7(b) and iscomplete in the state of FIG. 7(c), the trailing edge, TE, of thebarrier resin layer 101 b is located at a somewhat distant point on thedownstream side (located above in FIG. 10) just like the preform 101 ofFIG. 10(a). The length Lb from the center of the bottom 106 was 19.4 mm.

From a comparison of FIG. 6 with FIG. 7, it is found that at an Ls of14.5 mm shown in FIG. 6 and with a smaller rate of the PET resin Ra2supply, the barrier resin layer 101 b made of the barrier resin Rb islocated nearer to the inner peripheral surface of the preform 101, asshown in FIG. 6(c), than in the example shown in FIG. 7, due to theeffect of a slim, cylindrical shape of the barrier resin Rb.

Preforms were molded according to the injection pattern shown in FIG. 5by setting the forefront 20 p of the shut-off pin 20 shown in FIG. 3 atfive positions Ls of 14.00 mm, 14.55 mm, 14.60 mm, 15.10 mm, and 18.00mm in a period ranging from ts1 to ts2. The preforms in examples 1 to 5were measured for the length La of the leading edge, LE, and the lengthLb of the trailing edge, TE, and the biaxially stretched, blow moldedbottles made from these preforms were measured for oxygen transmissionrate (OTR cc/day). FIG. 8 is a table compiled from the results ofmeasurements for La, Lb, and OTR for each Ls. In the cases of Examples 2to 4, only the position Ls was changed in the pattern of FIG. 5.Meanwhile, in Example 1, time ts1, i.e., a time when the forefront 20 pis located at a position Ls of 14.00 mm in the pattern of FIG. 5, is setat a middle point between tb1 and tb2, i.e., a time zone where thebarrier resin Rb is supplied. FIG. 9 is a front view of the biaxiallystretched, blow molded bottle. The bottle 201 has a neck 202, a neckring 203, a tapered shoulder 204, a cylindrical body 205, and a bottom206, and has a total height of 160 mm. The body 205 has an outerdiameter of 70 mm. Oxygen transmission rate for the bottle 201 wasmeasured at 23 degrees C. and an oxygen partial pressure of 21%, usingOX-TRAN10/50 of Modern Controls, Inc.

In Example 1 where Ls is 14.00 mm, the supply of the PET resin Ra2 fromthe inner flow channel 15 e is shut down from time ts1 on when theforefront 20 p is located at position Ls. Therefore, the barrier resinlayer would take a slim, columnar shape in the vicinity of the trailingedge of the barrier resin Rb, rather than a slim, cylindrical shape suchas shown in FIG. 6(a). As a result, the trailing edge, TE, wouldentirely cover the bottom 106 of the preform 101 in an encapsulatedstate show in FIG. 10(b). In this case, the bottle has a high oxygenbarrier property, as found by an OTR of 0.0026 cc/day, but since the gasbarrier resin layer 101 b covers the gate vestige 107, problems arisebecause a stretching rod may breaks through the inner PET resin layer101 a, or because the bottom 206 of the bottle 201 may deform. Theseproblems would lead to a low yield and low productivity. Even if thetrailing edge, TE, does not become continuous in the bottom 106 of thepreform 101, there will arise similar problems found in the case wherethe gas barrier resin layer 101 b entirely covers the gate vestige 107.Therefore, it is necessary for the trailing edge, TE, of the gas barrierresin layer 101 b to be located outside the outer peripheral edge of thegate vestige 107.

In Example 2 where Ls is 14.55 mm, the trailing edge, TE, has a positionof 5.0 mm on an average, and is located between the outer peripheraledge of the gate vestige 107 and a peripheral edge corresponding to alower end of an inner peripheral surface 105 p of the body 105, as shownin FIG. 1(b), with other factors being similar to the above embodiment.The bottle had an OTR of 0.0028 cc/day, which was similar to Example 1where Ls was 14.00 mm, and the bottom was encapsulated. In Example 3where Ls was 14.60 mm, the length Lb of the trailing edge, TE, was 11.5mm, and the bottle had an OTR of 0.0075 cc/day. In Example 4 where Ls is15.10 mm, the length Lb of the trailing edge, TE, was 15.9 mm.

Example 5 having an Ls of 18.00 mm is a comparative example described inFIG. 7. In this case, the length Lb of the trailing edge, TE, was 19.4mm, and the OTR was 0.0236 cc/day. As compared to Example 2 having an Lsof 14.55 mm, the OTR was about 8.5 times as much as that of Example 2.It is found in this case that the oxygen barrier property has decreasedto a large extent. Example 5 has the OTR about 3 times as much as theOTR of Example 3 having an Ls of 14.60 mm. On the contrary, even at anLs of 14.60 mm with the trailing edge, TE, having the length Lb of 11.5mm, it is found that the bottle would have a considerably better oxygenbarrier property, as compared to any conventional molding process.

As regards the leading edge, LE, of the gas barrier resin layer 101 b,the length La of the leading edge, LE, is found to decrease graduallyfrom 21.7 mm to 17.6 mm under the condition that the Ls ranges from14.00 mm to 18.00 mm. This La is a factor that can be controlled byadjusting the time interval between time ta1 and time tb1 in theinjection pattern of FIG. 5.

An overall comparison of five examples having an Ls in the range of14.00 mm to 18.00 mm reveals that slight displacement of the forefront20 p of the shut-off pin 20 leads to a large change in the length Lb ofthe trailing edge, TE, and that this change greatly affects the oxygenbarrier property of the bottle 201 molded under this change. Bycontrast, this indicates that according to the molding device of thisinvention, flow adjustment can be precisely achieved in quite a shortperiod of time, and the position of the trailing edge, TE, of thebarrier resin layer 101 b can be controlled in a high degree ofaccuracy, simply by sliding the shut-off pin 20 in a little bit ofmovement, combined with the use of a servomechanism for precisioncontrol of the position of the forefront 20 p of the shut-off pin 20.

This invention has been described above with respect to preferredembodiments, but it is to be understood that this invention should notbe construed as limitative to these embodiments. In the aboveembodiments, description was made on a preform having a laminarstructure of 2-resins/3-layers, in which the second-resin layercomprising a barrier resin is laminated with the main-resin layers madeof a PET resin, on an injection molding process and a molding device forinjection molding such a preform. However, this invention is not limitedto the 2-resin/3-layer laminar structure. Within a technical idea ofthis invention that the mode of laminating the main-resin layers withthe second-resin layer is controlled at high productivity and in a highdegree of accuracy, various other laminar structures are feasible, suchas a colored resin layer used as an intermediate layer for a decorativepurpose.

As regards the injection molding device, the device shown in FIG. 2 is amere example. Many variations can be used for the details of the device.Also as regards the injection molding process, the injection patternshown in FIG. 5. is only an example. For instance, according to thepattern of FIG. 5, the forefront 20 p of the shut-off pin 20 is moved toa position Ls after the injection starting time tb1 of the barrier resinRb, but the forefront 20 p can be moved to Ls before the injectionstarting time tb1 of the barrier resin Rb.

The main resin for molding the preform is not limited to the PET resin.Use can be made of the resins conventionally used in the biaxiallystretched, blow molded bottles, such as polypropylene. As the secondresin, not only gas barrier resins but also those resins having otherfunctions or resins for a decorative purpose can be used. As the gasbarrier resin, MXD6 nylon is used, but other nylon resins and ethylenevinyl alcohol copolymers (EVOH) can also be used.

INDUSTRIAL APPLICABILITY

The preforms obtained by using the injection molding device of thisinvention can be employed to produce those bottles having theintermediate layer, such as the barrier resin layer, laminatedespecially in the neighborhood of the bottom in a highly controlledmanner.

DESCRIPTION OF REFERENCE SIGNS

-   1. Mold-   2. Core mold-   3. Cavity mold-   4. Cavity-   5. Pin gate-   11. Nozzle section-   12 a, 12 b. Guide channel-   14 al 1, 14 a 2, 14 b. Manifold-   15 a. Outer flow channel-   15 b. Middle flow channel-   15 c. Inner flow channel-   15 as, 15 bs, 15 cs. Diameter-reduced flow channel-   17 c. Outlet-   19. Joined flow channel-   20. Shut-off pin-   20 p. Forefront-   21. First mandrel-   22. Second mandrel-   23. Third mandrel-   Ls0, Ls, Ls1. Position of the forefront of the shut-off pin-   Ra. Main resin (PET resin)-   Rb. Second resin (Barrier resin)-   Sa. First feeder-   Sb. Second feeder-   101. Preform-   101 a. Main-resin layer (PET resin layer)-   101 b. Second-resin layer (Barrier resin layer)-   102. Neck-   103. Neck ring-   105. Body-   105 p. Inner peripheral surface-   106. Bottom-   107. Gate vestige-   LE. Leading edge-   TE. Trailing edge-   La. Length to the leading edge-   Lb. Length to the trailing edge-   201. Bottle-   202. Neck-   203. Neck ring-   204. Shoulder-   205. Body-   206. Bottom

1. A preform in a test tube shape for biaxial stretching and blowmolding use, in which a second-resin layer serving as an intermediatelayer is laminated with main-resin layers that makes up a shape of thepreform, wherein a trailing edge of the second-resin layer is locatedwithin a range covering from outside of an outer peripheral edge of acircular gate vestige formed in the center of a bottom plate of a bottomto a lower end of a corresponding inner peripheral surface of a body.